For example, a liquid crystal panel used for a liquid crystal display device such as a liquid crystal television does not emit light, and thus a backlight unit is required as a separate lighting device. The backlight unit is known, which is placed behind the liquid crystal panel (on a side opposite to a display surface side). The backlight unit includes a chassis having an opening on a liquid crystal panel side surface, numerous light sources (for example, cold cathode tube) housed in the chassis as lamps, and an optical member (diffuser and the like) provided in the opening of the chassis and efficiently discharging light emitted from the light sources to the liquid crystal panel side.
When the light sources emit linear light in the backlight unit, the linear light is converted into planar light by the optical member to uniform brightness of illumination light. However, when the line light is not sufficiently converted into the planar lights, a linear lamp image is generated along arrangement of the light sources, which deteriorates display quality of the liquid crystal display device.
In order to achieve uniform illumination light in the backlight unit, for example, it is desirable that the number of the light sources to be arranged is increased to reduce a distance between the light sources that are adjacent to each other or a diffusivity of the diffuser is increased. However, when the number of the light sources is increased, cost of the backlight unit is increased, and power consumption is also increased. When the diffusivity of the diffuser is increased, brightness cannot be increased, which disadvantageously requires an increase in the number of the light sources at the same time. Then, a known backlight unit suppressing power consumption and maintaining uniform brightness is disclosed in the following Patent Document 1.
The backlight unit described in Patent Document 1 includes a diffuser provided in a floodlight direction of a plurality of light sources. A pattern of dots for modulated light is printed on the diffuser. The pattern has total light transmittance (opening ratio) of 62 to 71% and a haze value of 90 to 99%. Particularly, a diameter of a dot located immediately above each light source is great. The diameter of the dot is reduced as departing from each light source. According to such a configuration, light emitted from the light sources is efficiently utilized, and thereby light having sufficient and uniform brightness can be irradiated without increasing power consumption of each light source.    Patent Document 1: Japanese Unexamined Patent Publication No. 2005-117023